We use feature branches on a git repository running on a GitLab server; with a webhook to poll jenkins on the git repository. We've several branches:
master
develop
feature/A
feature/B
...
A user from doc team added some feature branches named with a capital letter:
Feature/C
Feature/D
...
From this point, our job configured to build our application on feature branches commit detection with pattern */feature/${FEATURE_BRANCH} always built the same branch feature/A even if changes were made in feature/B etc.

I reproduced the problem on a fresh git repository, reproducing a quick life of the repository; before the addition of Feature/C; everything ran fine. With the Addition of Feature/C; the problem occurred.

When both feature and Feature branches were present; the polling was triggered by GitLab but the detection of the origin branch of the commit does not work on jenkins.

I found as workaround to change my pattern from */feature/${FEATURE_BRANCH} to */*eature/${FEATURE_BRANCH} but I was expecting that even if feature branches were added starting with Feature instead of feature; the process would detect and get the commit on the right branch.

Some logs:

Example of bad detection (last commit was not on the feature/sync branch):

Cloning the remote Git repository
Cloning repository git@git1.eu.lcom:mobilite/CollectionAndroid.git
> C:\Progs\Git\bin\git.exe init c:\CI\workspace\LCatalog-android-feature-build # timeout=10
Fetching upstream changes from git@git.eu.lcom:mobilite/CollectionAndroid.git
> C:\Progs\Git\bin\git.exe --version # timeout=10
> C:\Progs\Git\bin\git.exe -c core.askpass=true fetch --tags --progress git@git1.eu.lcom:mobilite/CollectionAndroid.git +refs/heads/:refs/remotes/origin/
> C:\Progs\Git\bin\git.exe config remote.origin.url git@git1.eu.lcom:mobilite/CollectionAndroid.git # timeout=10
> C:\Progs\Git\bin\git.exe config --add remote.origin.fetch +refs/heads/:refs/remotes/origin/ # timeout=10
> C:\Progs\Git\bin\git.exe config remote.origin.url git@git1.eu.lcom:mobilite/CollectionAndroid.git # timeout=10
Pruning obsolete local branches
Fetching upstream changes from git@git1.eu.lcom:mobilite/CollectionAndroid.git
> C:\Progs\Git\bin\git.exe -c core.askpass=true fetch --tags --progress git@srdspgit1.eu.lcom:mobilite/CollectionAndroid.git +refs/heads/:refs/remotes/origin/ --prune
Seen branch in repository origin/Feature/FicheC
Seen branch in repository origin/Feature/Wording_13-01
Seen branch in repository origin/Feature/Wording_15-12
Seen branch in repository origin/Feature/account
Seen branch in repository origin/Feature/change-decsription-button
Seen branch in repository origin/Feature/change-tracking-ajustements
Seen branch in repository origin/Feature/change_tracking
Seen branch in repository origin/Feature/login
Seen branch in repository origin/Feature/remove-guava
Seen branch in repository origin/Feature/sync
Seen branch in repository origin/develop
Seen branch in repository origin/master
Seen branch in repository origin/masterv5r1
Seen 13 remote branches
Checking out Revision 5e63c5c7488bcdab1632467cc61bbae2dc67eb87 (refs/remotes/origin/feature/sync)
> C:\Progs\Git\bin\git.exe config core.sparsecheckout # timeout=10
> C:\Progs\Git\bin\git.exe checkout -f 5e63c5c7488bcdab1632467cc61bbae2dc67eb87
> C:\Progs\Git\bin\git.exe rev-list 5e63c5c7488bcdab1632467cc61bbae2dc67eb87 # timeout=10
No emails were triggered.
[EnvInject] - Executing scripts and injecting environment variables after the SCM step.
[EnvInject] - Injecting as environment variables the properties content
JAVA_HOME=C:\Progs\jdk-1.8.0_60

And the list of branches seen by Git command line; note that all feature branches are named with lower case names instead of the two Feature/Wording* branches:
$ git branch --list --all

• develop
  remotes/origin/HEAD -> origin/develop
  remotes/origin/develop
  remotes/origin/feature/FicheCad
  remotes/origin/feature/account
  remotes/origin/feature/advanced
  remotes/origin/feature/change-decsription-button
  remotes/origin/feature/change-tracking-ajustements
  remotes/origin/feature/change_tracking
  remotes/origin/feature/login
  remotes/origin/feature/remove-guava
  remotes/origin/feature/sync
  remotes/origin/Feature/Wording_11-01
  remotes/origin/Feature/Wording_15-12
  remotes/origin/master
  remotes/origin/masterv5r1