I'm attempting to summarize and review a new dataset using 'codebook' and am encountering an error. Specifically, certain variables throw an "options not allowed" r(101) error, despite my not (knowingly) using any options. Example code produces the same error (using my Stata 14 SE on Linux).

Code:
clear all
set obs 100
gen x=4
codebook
replace x=.a in 1
codebook
replace x=.b in 2
codebook 
replace x=.m in 3
codebook
replace x=.z in 4
codebook
expand 300 
codebook
It seems to be some combination of data size and the multiple different missing values; I can't seem to reproduce the error with one of those alone. Any idea what's causing this? Perhaps some memory or matsize error? But the demo dataset isn't very large...