I have gottten something similar to this. My friend and I were playing a game and we got the pacts researched and the relationship to the necessary level. My friend (TEC) gave me (Vasari) the supply pact. I accepted, and saw my available supply jump up by about 940 (I had the Vasari research for bonus fleet supply % done). However, despite having 940+ fleet supply showing as available in the top bar, any attempts to build ships failed as they were greyed out and showed as "Insufficent Fleet Supply".
EDIT: I should mention that this bonus fleet supply was in fact available for my friend to use however.