Cosmos 2258 decayed slowly until 950427, then normally. You can see that it was brought out of its operational orbit around 950224, decayed very slowly until 950427, when the decay rate suddenly increased by a factor of about 4, and decayed on 940608, after a normal decay phase that took 33 days from MM=15.90.
Figure 7: Mean motion for Cosmos 2258 as a function of time