Legend is displaying additional shape

Question

I'm using the following data frame:

df1 <- structure(list(Genotype = structure(c(1L, 1L, 1L, 1L, 1L,
2L,2L,2L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 1L, 1L, 1L,
1L,1L, 2L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L),
.Label= c("miR-15/16 FL", "miR-15/16 cKO"), class = "factor"), 
Tissue = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 
3L, 3L, 3L, 3L, 3L, 3L, 4L, 4L, 4L, 4L, 4L, 4L, 4L, 4L, 4L, 
4L), .Label = c("iLN", "Spleen", "Skin", "Colon"), class = "factor"), 
`Cells/SC/Live/CD8—,, CD4+/Foxp3+,Median,<BV421-A>,CD127` = c(518L, 
715L, 572L, 599L, 614L, 881L, 743L, 722L, 779L, 843L, 494L, 
610L, 613L, 624L, 631L, 925L, 880L, 932L, 876L, 926L, 1786L, 
2079L, 2199L, 2345L, 2360L, 2408L, 2509L, 3129L, 3263L, 3714L, 
917L, NA, 1066L, 1059L, 939L, 1269L, 1047L, 974L, 1048L, 
1084L)),
.Names = c("Genotype", "Tissue", "Cells/SC/Live/CD8—,,CD4+/Foxp3+,Median,<BV421-A>,CD127"),
row.names = c(NA, -40L), class = c("tbl_df", "tbl", "data.frame"))

and trying to make a plot using ggplot2 where box plots and points are displayed grouped by "Tissue" and interleaved by "Genotype". This seems to be working well, however, I'm noticing that in my legend, there is an additional "a" that is being overlaid with the shape.

library(ggplot2)
library(ggpubr)
color.groups <- c("black","red")
names(color.groups) <- unique(df1$Genotype)
shape.groups <- c(16, 1)
names(shape.groups) <- unique(df1$Genotype)

ggplot(df1, aes(x = Tissue, y = df1[3], color = Genotype, shape = Genotype)) +
  geom_boxplot(position = position_dodge(), outlier.shape = NA) +
  geom_point(position=position_dodge(width=0.75)) +
  ylim(0,1.2*max(df1[3], na.rm = TRUE)) +
  ylab('MFI CD127 (of CD4+ Foxp3+ T cells') +
  scale_color_manual(values=color.groups) +
  scale_shape_manual(values=shape.groups) +
  theme_bw() + theme(panel.border = element_blank(), panel.grid.major = element_blank(),
                     panel.grid.minor = element_blank(), axis.line = element_line(colour = "black"),
                     axis.title.x=element_blank(), aspect.ratio = 1,
                     text = element_text(size = 9)) +
  stat_compare_means(label = 'p.format', method = 't.test',
                     label.y = c(0.1*max(df1[3], na.rm = TRUE) + max(df1[3][c(1:10),], na.rm = TRUE),
                                 0.1*max(df1[3], na.rm = TRUE) + max(df1[3][c(11:20),], na.rm = TRUE),
                                 0.1*max(df1[3], na.rm = TRUE) + max(df1[3][c(21:30),], na.rm = TRUE),
                                 0.1*max(df1[3], na.rm = TRUE) + max(df1[3][c(31:40),], na.rm = TRUE)))

If I hide the scale_color_manual legend, it removes the "a"s but it also removes the color from the legend. Am I missing something?

Thanks for any help!