I've never seen this issue then. I'm in week 12 and I reset my subs back to 50. Then I just went through the first 5 formations and subbed in a new guy at every position until I used 50 subs. All 50 subs worked perfectly well and it wasn't until I had used all 50 that I was told I couldn't do it anymore.
Every time I've ever reset my subs it has given me all 50 subs to use again. This is not just a display thing for me on my Xbox as I can then actually make 50 subs again.