We have a library loaded dynamically in Pipeline script with 

library "mylib@8c8a4a95f3187b82112cc2eb8539ba470c1eebff"

the sha1 in question is tagged on the remote, but not contained in any branch

Jenkins fails to load the library:

Loading library mylib@8c8a4a95f3187b82112cc2eb8539ba470c1eebff
Attempting to resolve 8c8a4a95f3187b82112cc2eb8539ba470c1eebff from remote references...
> git --version # timeout=10
using GIT_SSH to set credentials Jenkins Account
> git ls-remote -h ssh://git@our-bitbucket.com:7999/libProject/mylib.git # timeout=10
Could not find 8c8a4a95f3187b82112cc2eb8539ba470c1eebff in remote references. Pulling heads to local for deep search...
> git rev-parse --is-inside-work-tree # timeout=10
Setting origin to ssh://git@our-bitbucket.com:7999/libProject/mylib.git
> git config remote.origin.url ssh://git@our-bitbucket.com:7999/libProject/mylib.git # timeout=10
Fetching origin...
Fetching upstream changes from origin
> git --version # timeout=10
> git config --get remote.origin.url # timeout=10
using GIT_SSH to set credentials Jenkins Account
> git fetch --tags --progress origin +refs/heads/:refs/remotes/origin/
> git rev-parse 8c8a4a95f3187b82112cc2eb8539ba470c1eebff^{commit} # timeout=10
> git branch -a -v --no-abbrev --contains 8c8a4a95f3187b82112cc2eb8539ba470c1eebff # timeout=10
Could not find a branch containing commit 8c8a4a95f3187b82112cc2eb8539ba470c1eebff
[Bitbucket] Notifying commit build result
[Bitbucket] Build result notified
ERROR: No version 8c8a4a95f3187b82112cc2eb8539ba470c1eebff found for library mylib