xts microsecond issue

Question

Saved an xts object in .RData file and then opened it again in another R instance. I lose the microsecond timestamp. I keep the same configs in both environments including digits.secs=6.

yum <- structure(c(262, 262, 262, 100, 100, 100, 120, 370, 370, 370, 367, 392), 
                 class = c("xts", "zoo"), 
                 .indexCLASS = c("POSIXct", "POSIXt"), 
                 tclass = c("POSIXct", "POSIXt"), 
                 .indexTZ = "UTC", tzone = "UTC", 
                 index = structure(c(1355821310.69496, 
                                    1355821310.73023, 1355821310.75223, 
                                    1355821310.8355, 1355821310.87186,
                                    1355821310.88684), 
                 tzone = "UTC", 
                 tclass = c("POSIXct", "POSIXt")), 
                 .Dim = c(6L, 2L), 
                 .Dimnames = list(NULL, c("SzX", "SzS")
                )
              )

Any pointers?