If you try to sync to a label, the p4-plugin syncs to latest changelist instead.
This does not happen in p4plugin 1.9.7
Output from same client, different version of plugin
p4-plugin 1.10.0
P4 Task: syncing files at change: 230943
p4 sync -q /auto/wksp/test_client/...@230943
duration: 0m 26s
p4-plugin 1.9.7
p4 label -o REL_XXX +
P4 Task: syncing files at client/label: REL_XXX
p4 sync -q /auto/wksp/test_client/...@REL_XXX +
00:00:39 duration: (280ms)
Note that there is no p4 label -o REL_XXX output for p4-plugin 1.10.0