If $string or $issn is passed to GetSubscriptions, the request is false.
See Bug 5864, especially the last comment from Frédérick Capovilla.
I have made a patch to solve this problem.
Created attachment 6075 [details] [review]
Patch from BibLibre
Created attachment 6180 [details] [review]
Signed off patch
Ok, the query now looks more consistent, and works as expected. Signed off.
QA: Looks good. Marked as Passed QA.
patch pushed, please test
Included in 3.6 prior to 3.6.5.