Back in the 1980s when the Texas Public Employees Association was negotiating with the legislative leaders for pay raises they made a concession for a smaller raise, but in return they had language inserted into the law so that state employees would receive a minimum interest rate of 5% on their share of the pensions. If they had not worked to get that legislation passed, then the state could have contributed even less to the pension system. Nobody expected interest rates to drop as low as they have been over the last ten years so it has been a plus for state employees; however, it does increase the unfunded liabilities faced by ERS. There has been talk of having new employees enter into a 401k type program, but I do not believe that has been adopted into law.
FWIW, I do not believe that the teachers retirement system has a similar deal and they are much more seriously underfunded than ERS.